We describe a method for improving the precision of metasearch results based upon scoring the visual features of documents' surrogate representations. These surrogate scores are used during fusion in place of the original scores or ranks provided by the underlying search engines. Visual features are extracted from typical search result surrogate information, such as title, snippet, URL, and rank. This approach specifically avoids the use of search engine-specific scores and collection statistics that are required by most traditional fusion strategies. This restriction correctly reflects the use of metasearch in practice, in which knowledge of the underlying search engines' strategies cannot be assumed. We evaluate our approach using a precision-oriented test collection of manually-constructed binary relevance judgments for the top ten results from ten web search engines over 896 queries. We show that our visual fusion approach significantly outperforms the rCombMNZ fusion algorithm by 5.71%, with 99% confidence, and the best individual web search engine by 10.9%, with 99% confidence.

Prior research into search system scalability has primarily addressed query processing efficiency [1, 2, 3] or indexing efficiency [3], or has presented some arbitrary system architecture [4]. Little work has introduced any formal theoretical framework for evaluating architectures with regard to specific operational requirements, or for comparing architectures beyond simple timings [5] or basic simulations [6, 7]. In this paper, we present a framework based upon queuing network theory for analyzing search systems in terms of operational requirements. We use response time, throughput, and utilization as the key operational characteristics for evaluating performance. Within this framework, we present a scalability strategy that combines index partitioning and index replication to satisfy a given set of requirement.

Color histograms are used to compare images in many applications. Their advantages are e#ciency, and insensitivity to small changes in camera viewpoint. However, color histograms lack spatial information, and this can cause images with very different appearances to have similar histograms. For example, a picture of fall foliage might contain a large number of scattered red pixels; this could have a similar color histogram to a picture of a single large red object. We describe a histogram-based method for comparing images that incorporates spatial information. While a color histogram counts the number of pixels with a given color, a color coherence vector #CCV# measures the spatial coherence of the pixels with a given color. If the red pixels in an image are members of large red regions, this color will have high coherence, while if the red pixels are widely scattered it will havelow coherence. CCV's can be computed at over 5 images per second on a standard workstation. A da...

Color histograms are widely used for content-based image retrieval. Their advantages are efficiency, and insensitivity to small changes in camera viewpoint. However, a histogram is a coarse characterization of an image, and so images with very different appearances can have similar histograms. We describe a technique for comparing images called histogram refinement, which imposes additional constraints on histogram based matching. Histogram refinement splits the pixels in a given bucket into several classes, based upon some local property. Within a given bucket, only pixels in the same class are compared. We describe a split histogram called a color coherence vector (CCV), which partitions each histogram bucket based on spatial coherence. CCVs can be computed at over 5 images per second on a standard workstation. A database with 15,000 images can be queried using CCVs in under 2 seconds. We demonstrate that histogram refinement can be used to distinguish images whose color histograms are indistinguishable.